I think I know what is meant, but somehow it reads backwards. Is D65 not a standard illuminant specified by a spectral emission (range) of visible wavelengths (colors); and is not 6500K a color temperature specified by a single color?

picky, picky . . .

D65 is an exact description of a color but it's design was built upon many, many measurements made around the world and averaged. But if you plot it on the CIE chromaticity diagram, it falls within a single area on the black body curve. That isn't the case with 6500K. You'll see below, the lines of correlated color temp running magenta to green. ANY color there can be said to be 6500K.

Is D65 not a standard illuminant specified by a spectral emission (range) of visible wavelengths (colors); and is not 6500K a color temperature specified by a single color?

No...D65 is a very specific combination of amber/blue & magenta/green which specifies a single color temp colors...6500ºK is the point in the amber/blue wavelengths but has no specific info for the magenta/green tint. So, 6500)K can refer to a range of colors where D65 refers to a single specific color.

No...D65 is a very specific combination of amber/blue & magenta/green which specifies a single color temp colors...6500ºK is the point in the amber/blue wavelengths but has no specific info for the magenta/green tint. So, 6500)K can refer to a range of colors where D65 refers to a single specific color.

Thanks Gents,

Sorry about that I was confusing the use of "D65" as a unique color in this topic with CIE's use of "D65" as a standard illuminant.

I was confusing the use of "D65" as a unique color in this topic with CIE's use of "D65" as a standard illuminant.

I think everyone is in basic agreement here, but the terminology has possibly led to a little confusion. To put what is possibly too fine a point on it, it's probably better to say that D65 has a color than to say that D65 is a color. D65 is a specification of a power spectral density, and thus exists without reference to the visual system of humans. The concept of color is limited to animal visual systems, and, if unqualified, to the human visual system. Humans (except for a few percent of the male population and a much smaller part of the female population) perceive light with a D65 spectrum as having a certain color. However, many other spectra (an infinite number of them) have the same color -- a single set of tristimulus values. The other spectra that have the same tristimulus values and look the same to humans are called the metamers of D65.

Maybe. Keep in mind that any Kelvin value is a range of colors. D65 is a specific color, 6500K is a range. The type of lighting too can play a huge role. A 6500K Fluorescent with the spiky spectrum may produce a vastly different color appearance than a Solux with a similar spec for Kelvin. Add OBA's into the mix, you'll soon find that such values are not really useful. Getting a screen to print match is and often, differing values end up producing this goal.

Perhaps you misstated yourself.

Techno-geek Warning

* Skip this section if you aren't into technical discussions, you won't miss any real-world information!

Since you are wanting to be SO specific, both D50 and 5000K refer to spectrums of visible light. D50 is part of the Standard Illuminant series D standard. It is, "A standard illuminant (which) is a theoretical source of visible light with a profile (its spectral power distribution) which is published" (emphasis mine)(1).

I can see how someone can confuse D50 as being a specific color because of the chart below:

(Credit: Wikipedia)

The D65, D50, etc. "spots" on the CIE X,Y "horse shoe" is a transformation of a spectrum power distribution (SPD) (from ~300-700nm, the visible light spectrum) to a specific point in the CIE XY color space "horse shoe"(2).

For all practical purposes, saying that D50 and 5000K (for print) are equivalent is essentially correct due to the nature of their SPD's being almost a match. In fact, in the Wikipedia article on Illuminant D65(3) it says:

"As any standard illuminant is represented as a table of averaged spectrophotometric data, any light source which statistically has the same relative spectral power distribution (SPD) can be considered a D65 light source. There are no actual D65 light sources, only simulators..."

and

"[D65] is intended to represent average daylight and has a correlated colour temperature of approximately 6500 K."

You can see the relationship between different series D Illuminants and their relative black body correlated color temperatures (from 4000K to 25000K) in the chart below:

(Credit: Wikipedia)

Because of this, D50 and 5000K are essentially (statistically) the same. I want to repeat that while there are D50 and 5000K "dots" on the CIE XY horse shoe, which appear as specific "colors", these values represent a transform of SPD's of light colors (wavelengths) to force it to fit into a two dimensional, XY, diagram and it is only the spectrum of colors that creates "white" because "white" is NOT a color frequency (like it is implied in the CIE XY diagram), it is a combination of colors (i.e. a spectrum of colors).

This is why they call 5000K a "correlated color temperature" to D50. Frankly, trying to match spectrums is a rather overwhelming and confusing idea to most non technicians, as opposed to "only" have to match a specific color temperature, even if that color temperature does imply a matching spectrum.

Functionally, this means that any 5000K light source will work as a viewing source for proofing prints!

SoLux

* You can skip this section if you are more interested in real world light booths...

No pre-press or print shops I have seen or know of use any type of incandescent light source. Not even something like the SoLux 3500K, 4100K, or 4700K halogen light source.

While I have perused the SoLux web site and see they are big with art galleries/museums, we need to keep in mind that art galleries are far different than print shops.

By definition, art galleries are interested in (1) presenting an artistic representation of something (e.g. the artistic representation might be a painting) and (2) protecting that representation from potential damage (e.g. from lighting sources). So while SoLux's products may be very appropriate for viewing original art, that is very different from accurate (and consistent between locations) reproduction of reflective source materials (and their relative spectral power distributions) and avoiding metamerismic errors in reproduction that, for example, pre-press and print shops must do.

As a practical matter, to get even lighting, you would have to have a number of incandescent lights to cover any reasonable light booth area and they produce A LOT of heat. Many pre-press viewing booths are on press floors which are not air conditioned. Because of this, many get VERY hot during the summer months and an incandescent light booth (effectively a heating oven with ~90% of its energy being converted to heat) would be impractical.

While early florescent lights did have some nasty "spiky spectrums" (the infamous "green cast" problem), this is much less of an issue now. Even over the last 10 years, manufacturers have gotten much better at matching the necessary phosphors to get a usable spectrum of light at any particular color temperature. Practically, this means that a Home Depot 5000K florescent bulb, a specialty "full spectrum" florescent bulb, and the $5000+ Xrite SpectraLight III lighting booth will produce the same results.

Also, SoLux's emphasis is on CRI accuracy, which may or may not accurately represent the relative spectral power distributions of a printed proof or its source standard, D50. As Jim mentioned, there are many metamers of the Illuminant series D standards as represented in the CIE XY diagram, but only one that is used as the correct SPD in the D50 standard. Depending on the SPD of these alternative spectrums they may or may not be practically different. Also, you shouldn't confuse Color Rendering Index (CRI), which is based on Illuminant series F lighting values(1) with equivalents to Illuminant series D SPD values.

In The Real World

***** This is the section you should pay attention to if you want to duplicate what pre-press (including magazines and newspapers) and print shops (even ad agencies) are using in the real world!

In the real world, pre-press and prints shops where they are comparing the press prints vs. the digital proofs (95+%) is done with 5000K florescent lights in a viewing box. 5000K florescent lights are the standard.

Because of this, even if the SoLux (and other) lights were "more accurate" SPD representations, they will still be different than what is used in the vast majority of lighting booths (and transparency light tables)... 5000K florescent lights. You can verify this for yourself by visiting a few local print shops to see what they are using. There is likely far more of a difference between a halogen 4700K (300 degrees Kelvin off the standard) light source and a super high quality light booth (e.g. Xrite SpectraLight III at $5000+(5),(6)) than there is between a Home Depot 5000K florescent and that same light booth.

Even if there were no effective difference between the three, there are cost considerations that make florescent lighting the preferred choice (equipment and electrical).

It is both relatively easy and inexpensive to make your own print proofing light booth using florescent lighting. I would imagine that someone with some tools, time, and imagination could make a serviceable light booth with 2', 3', or 4' (depending on size of proofs) florescent light fixtures for <$250 (certainly less than $500). "All you need" is some plywood (box); 2x4's (legs and structure to nail the plywood to); reflective white (without coloration) siding and/or paint ("white" should reflect almost all of the light that hits it so just about any "pure white" should work); one or more two-bulb florescent fixtures; ; miscellaneous wiring, switch(es), nails, screws, etc.; and a bit of time.

Back to the OP's initial questions/problem

Anyway, back to the OP's problem: How can he be sure that his customers will view his work in the way he intends them to?

First, which he already appears to have in hand, is to have a calibrated monitor which he uses to make any necessary adjustments so that his work meets his artistic/aesthetic requirements regarding appearance (assuming compositional issues were resolved at the time of taking the pictures).

Second, he needs to have a way to ensure that when his customers print his work so that what they see is substantially what he is seeing on his end. To that second end, I suggested (a) ensuring that he was viewing his printed results in a 5000K light booth/environment and (b) to send a copy of his printed proof along with the digital file so they can ensure that their printed and/or ripped/pre-press results match his proof. Because most print proof lighting booths use florescent lighting, it behooves him to use florescent lighting in his booth as well. Of course, I say "booth", when that may only mean an overhead florescent light fixture (two to four 2'-4' 5000K florescent bulbs) in a light controlled, white walled room.

The pre-press industry has been dealing with these issues for longer than you or I have and it is well known/understood how to set up a proper viewing environment, even on the cheap.

Other Stuff

Frankly, I hadn't intended to get into this level of detail. I had thought people would not have started "picking fly manure out of the pepper" (you end up with all fly manure and no pepper) and used it as the basis for establishing how to properly go about setting up a viewing/proofing environment and/or workflow so the OP could ensure his customers saw his work as he did, especially if he doesn't have a photospectrometer. While theoretically interesting, this discussion probably doesn't help the OP with his goal.

Oh, an additional point. @digitaldog - You mentioned that, "Getting a screen to print match is and often, differing values end up producing this goal." The issue you are describing is one of metamerism of which lighting is only one component.

"The appearance of surface colors is defined by the product of the spectral reflectance curve (paper/inks - Scott) of the material and the spectral emittance curve of the light source shining on it. As a result, the color of surfaces depends on the light source used to illuminate them."(4)

Overcoming just the difference between emmissive light (monitor) and reflected light (print) can be difficult. From the sound of it though, letting Photoshop handle the color may be part of the problem, especially if he also has the OS/printer handling it (a "double whammy"), which could result in the over saturation problem he describes. One or the other probably need to be turned off, maybe even both.

Perhaps you can suggest a workflow that can help him with this process?

Finally, regarding why the original poster's pictures look more "washed out" on the web I can think of a couple reasons.

First, is the web browser color managed (I believe the latest version of Safari is)? Some are capable, but not all of those have color management turned on (Firefox).

Second, does he know that the destination is not recompressing them and/or doing additional processing that is changing its appearance. Even something as small as sharpening and/or recompression (to change the compression ratio) can have a detrimental effect on the appearance of photographs. I wonder if he has tried bringing those photos back into Photoshop to see if they still look washed out compared to the original? If so, the problem is on the other end. If not, then the problem is probably browser related.

If anyone has references that could correct a misunderstanding I have I would, sincerely, like to see those references!

The D65, D50, etc. "spots" on the CIE X,Y "horse shoe" is a transformation of a spectrum power distribution (SPD) (from ~300-700nm, the visible light spectrum) to a specific point in the CIE XY color space "horse shoe"(2).

Indeed. Now what about the that perpendicular line on the graph that is labelled 5500?

Quote

"As any standard illuminant is represented as a table of averaged spectrophotometric data, any light source which statistically has the same relative spectral power distribution (SPD) can be considered a D65 light source. There are no actual D65 light sources, only simulators..."

I allude to that.

Quote

No pre-press or print shops I have seen or know of use any type of incandescent light source. Not even something like the SoLux 3500K, 4100K, or 4700K halogen light source.

Neither have I. But the audience here by and large isn't prepress. And they can select and recommend to their clients, a more ideal product to use such as Solux.

Quote

While I have perused the SoLux web site and see they are big with art galleries/museums, we need to keep in mind that art galleries are far different than print shops.

Exactly. Though if I had my preferences in print shops, it be Solux. I'm working now in some print shops using digital presses using papers with enormous amounts of OBA's and the Fluorescent lights are not helping!

Quote

As a practical matter, to get even lighting, you would have to have a number of incandescent lights to cover any reasonable light booth area and they produce A LOT of heat.

There are a few good recipes for building great Solux viewing booth and they can produce very even coverage but heat is a factor. They only make Fluorescent booth's so big!

Quote

Practically, this means that a Home Depot 5000K florescent bulb, a specialty "full spectrum" florescent bulb, and the $5000+ Xrite SpectraLight III lighting booth will produce the same results.

IOW, some fluorescent bulbs suck less than they used to. <G>.

Quote

Oh, an additional point. @digitaldog - You mentioned that, "Getting a screen to print match is and often, differing values end up producing this goal." The issue you are describing is one of metamerism of which lighting is only one component.

Yes but again, the numbers that produce a visual match are the correct numbers. They often do match what we expect or assume to be the right number: calibrating a display at CCT 5717K to match a GTI box that we're told is "5500K".

First, is the web browser color managed (I believe the latest version of Safari is)? Some are capable, but not all of those have color management turned on (Firefox).

Here's an easy way for anyone who cares to find out if their web browser is color-managed. Ignore the data at the end; it's really old. Firefox 20.0.1 has color management turned on by default; at least it's on in my copy, and I never messed with the settings.

Yes, I'm sure. But, on rechecking, although Sigma Photo Pro had embedded the profiles OK, stupid FastStone Viewer - which had I used to crop the images, stripped the profiles out and there they were . . . gone

. . . well, the previous images now have profiles and should all look the same unless your browser is not "color managed" . .

Yes, this order looks correct assuming Explorer because it's no color managed...sRGB and Adobe RGB should be pretty close because both color spaces assume D65 and close to 2.2 gamma (sRGB is a tuned gamma not a straight power curve). PP RGB's color is also way far away from the other two color spaces. So, what you see is expected (sadly).

Indeed. Now what about the that perpendicular line on the graph that is labelled 5500?

I assume you are referring to the line that is labeled "5000K", not "5500"?

I included the link from Wikipedia to show the relationship between the Illuminant series D values and related black body temperatures in Kelvin. As to why they showed lines and not also points, I can only guess. If it were me, I'd do it because while "D50" is very short and the space between different "D" values is wide enough for that text to fit in a limited size chart, the same cannot be said for the various values of the black body temperatures (e.g. 5000K, 6500K, etc.).

My take on this is that it is the point of intersection between the curved line and the straight line, which shows the closeness of the black body correlated color temperature (CCT) and that of the theoretical "D" series Illuminant. Other color space examples on the Wikipedia site show various charts, some with only the "D" series Illuminant "spot" on the chart; some with both the curved line and "spot"; and some with the "spot", curved line, and dots on the curved line showing CCT's (CIE 1931).

None of these charts are annotated as to what every part means, so your interpretation may be as good as mine. However, I would not assume that they are indicative of a spectrum power distribution (SPD) because, as can be seen on the animated .gif a bit further down in my previous reply, the SPD's are not linear.

As a quick aside, in my previous reply I had also noted the inherent difficulty in matching emmissive monitors to reflective prints and the graphic below illustrates this (for anyone who is interested):(8 )

Neither have I. But the audience here by and large isn't prepress. And they can select and recommend to their clients, a more ideal product to use such as Solux.Exactly. Though if I had my preferences in print shops, it be Solux. I'm working now in some print shops using digital presses using papers with enormous amounts of OBA's and the Fluorescent lights are not helping! There are a few good recipes for building great Solux viewing booth and they can produce very even coverage but heat is a factor. They only make Fluorescent booth's so big! IOW, some fluorescent bulbs suck less than they used to. <G>.

I'm taking these together because they are so closely related.

You are right that the audience here isn't, generally, pre-press, but the CYMK technologies are. At the least, they have their roots there. And, if you want to get your work published (self-publication aside), ultimately, it will have to be put into a pre-press/pressroom context. So, rather than try to create a new system, IMO, we should use the well-established, and perfectly functional, knowledge base of the pre-press/printing industries. Because of this, 5000K fluorescent is the standard proofing environment.

However, let's ignore this for a moment and take a look at the "fine art" printing market in which you do bring up an issue worth addressing. Unfortunately, I can't help but feel that perhaps you are approaching this from the wrong side. OBA's, by their nature, will increase metameric mismatch (corrected thanks to @digitaldog's post below) in most common viewing environments.(1)

For better or worse, depending on your viewpoint, (any type of) incandescent lighting is at the end of its life cycle here in the US and, for that matter, the rest of the world. While LEDs will probably become the dominant light source some time in the future, it is fluorescent lighting that currently rules. In the overwhelming majority of viewing environments, fluorescent lighting is what will be used to light fine art prints in the home.

Because of this, the issues you (correctly) decry regarding OBA's will not change, even if the printing world were to adopt halogen lighting like the SoLux (ignoring for a moment that they are 4700K lights rather than the needed 5000K for proper proofing). The rest of the world uses fluorescent lighting and therefore you will have to deal with the OBA issue.

You "can't fight city hall". By this, I mean that for the next 10-20 years fluorescent lighting will be the dominant lighting source, so OBA's will have to be dealt with.

The question is, "How?" IMO, the answer to this is to do my printing with OBA-free paper, which is readily available.(6) Yes, I understand that this may reduce apparent brightness and apparent gamut in the prints. However, I believe that the benefits far outweigh the problems.

First, when you view paper with OBAs in (or on) it under halogen lights to avoid UV light from fluorescing the OBAs, you are neutralizing the OBAs, therefore making that paper appear as though it didn't have OBAs in it. At this point, you are making paper with OBAs appear to be OBA-free paper. If that is what you want, then just cut out the OBAs and use OBA-free paper from the start and you eliminate this metameric mismatch source.

Second, while it is currently unclear as to exactly how quickly OBAs deteriorate, the fact is that they do.(2),(5),(7) As OBAs deteriorate, the paper moves closer and closer to that of an equivalent OBA-free paper. If you were able to come up with an appropriate OBA color profile in your prints (under fluorescent lights), then the colors you wanted when the prints were new will now shift over time. If you had an OBA paper color profile under, say, the SoLux, then your printed colors would frequently be the wrong colors under the common fluorescent lighting (time of day and amount of daylight) and would only move over time to your intended colors.

"Fine art" printing has its own set of issues(3),(4) and lighting is certainly one of them. In my mind, one of the problems we can't fight right now is lighting. Far easier, and one which there are readily available products for, is to use OBA-free paper and then the lighting related metameric mismatch inherent in OBA paper becomes a non-issue ("OBA-associated Risk").(2) Fortunately, OEM ink manufacturers (e.g. Epson, HP) have put a tremendous amount of resources into trying to eliminate the effects of lighting on their ink colors over the last couple decades, so ink-related metameric mismatch is minimized.

You also mention that, "They only make Fluorescent booth's so big!". True, but you refer to "a few good recipes for building great Solux booth", so, to be fair, you could apply your own "recipe" and build an equivalent fluorescent booth to just about any size imaginable. Fluorescent bulbs are available up to 8 feet in length, though "good" bulb availability (i.e. not industrial) is probably more practically limited to 4 feet. Using some combination of 2', 3', 4', and 8' fluorescent bulbs, I cannot imagine a size limitation that would be present in a fluorescent booth that would not also exist with an equivalent halogen booth... without the "Easy Bake Oven(TM)" effect.

Yes but again, the numbers that produce a visual match are the correct numbers. They often do match what we expect or assume to be the right number: calibrating a display at CCT 5717K to match a GTI box that we're told is "5500K".

While reading your comment above, it made me think of another issue that hasn't been been discussed (in this thread, at least). In the home (and many galleries/museums), the viewing environments will likely be using lighting that is in the 2700K to 4200K range (most likely around 3500K). While metameric mismatch is fairly well controlled with OBA-free paper and OEM inks, the artistic/aesthetic appearance still needs to be considered in the final prints.

However, possibly more important is the issue of light intensity (Lux)(9) in the viewing environment. While a print may look aesthetically correct in a bright viewing booth, in the relatively dim environment of the home (without specific "art gallery" lighting), it may lose a substantial amount of its apparent detail and/or vibrance/saturation. And I understand you are aware of these issues!(10)

For better or worse, ultimately, any "art" should probably be prepared such that it still "communicates" what its creator intended in its "final resting place". I'm not going to go much further into this because my brother has some software printing products he will be releasing in the next year or so that can help address these issues.

Regardless, I hope this discussion is still in the same approximate ball park as the OP's initial question. Anyway, this is probably a discussion for another thread/place/time...

I've spent much more time than I expected on this thread, interesting as it has been, and need to get back to "my day job" and get back to "lurking" around here. Thanks!

My apologies for diverting from the original topic. While the discussion is related, I'm not sure it is helping the OP with his problem.

(Disclaimer: I have no financial or other interest in any of the companies represented in the links above. They are provided solely for illustrative/informative purposes unless otherwise indicated. And, as Jim Kasson apologized, I'm sorry for being a bit (overly?) pedantic.)

Note: I edited the above post to clarify that references to "metamerism" should have been, more accurately, "metameric mismatch". All terms have been corrected to keep the point both correct and consistent.)

OBA's, by their nature, will increase metamerism in most common viewing environments.(1)

What Harold says there about Metamerism is correct as is his term of the opposite and undesirable: metameric mismatch (also known as metameric failure). That said, I don't understand how OBA's increase metamerism but wouldn't that be a good thing? The article seems to express the opposite opinion.

@digitaldog - Sorry, you are correct, I had another brain fart. Half of my last post was written after midnight last night and I wasn't firing on all cylinders. What I meant was "increase metameric mismatch"...

I think you got the gist of my point, even if my proof-reading skills are sometimes (often) lacking. I guess that is one of the reasons I attach references so that in case I make a mistake like that, the real meaning can be found in the article.

@digitaldog - Sorry, you are correct, I had another brain fart. Half of my last post was written after midnight last night and I wasn't firing on all cylinders. What I meant was "increase metameric mismatch"...

Which is why OBA's and the viewing conditions are kind of important. Fluorescent lights are not at all ideal here, they can produce an ugly color cast. And lots of prepress operations are using papers with high OBA's (although in the past, this was rare). I'm working with a client running a digital press, using a paper with a Bstar value of over -6!

Which is why OBA's and the viewing conditions are kind of important. Fluorescent lights are not at all ideal here, they can produce an ugly color cast. And lots of prepress operations are using papers with high OBA's (although in the past, this was rare). I'm working with a client running a digital press, using a paper with a Bstar value of over -6!

I agree with you. However, I'm just adverse to beating my head against a wall.

OBA's are a reality for many people. As I know you know, but it is worth stating to be clear, OBAs are there to make paper appear brighter by taking available UV light and "fluorescing" it into visible wavelengths (the "blue" part of the spectrum).(1)

Simply put, you and I have different approaches to how to deal with the OBAs. Succinctly, I believe:

1. Incandescent lighting is going the way of the Do-do bird and fluorescent lighting is/has replaced it in the short term (next 10+ years) and LED lighting is currently the most likely replace both in the long term (15+ years). Because of this:

OBA proofs "matched" under incandescent lighting will likely exhibit metameric mismatch in the real world where the resulting prints will be viewed under fluorescent lights.

I'm not willing to beat my head against this "wall" (the change away from incandescent lighting). I see it as a losing battle and that there are more important battles to be fought.

2. Because of its nature, I see only two practical choices in dealing with OBA paper (for "fine art" related prints):

Deal with all of the shortcomings of OBA paper and create the best possible profiles under fluorescent lighting. (least preferable)

Educate the pre-press/print shops that, for "fine art" printing, OBA-free paper is the appropriate choice to avoid most of the headaches (OBA associated Risk) associated with OBA paper. (preferred approach)

3. Because of #1 and #2, I would rather try to explain to pre-press/printer customers that OBA paper has the above mentioned problems that can be solved by using OBA-free paper and that:

OBA paper will fade over time, causing color shifts in the prints and paper.

OBA-free paper will not fade (in that way) and will not cause color shifts over time.

OBA paper will exhibit an immediate color shift when viewed under a mismatched lighting source (e.g. proofed under fluorescent lights, but viewed under incandescent/LED) and leaves the pre-press/print shop open to problems of metameric mismatch (OBA associated RISK).

4. OBA paper may well be appropriate for various books, graphic novels, newspapers, non-photographic quality magazines, printing charts, and text printing (printing where color fidelity is not mandatory, but "impact" is).

5. Even with the many theoretical benefits of using incandescent lighting, using it effectively turns OBA paper into OBA-free paper. Why not just cut out the "middle man" and start with OBA-free paper and then you don't have to worry about metameric mismatch in the destination viewing environment?

6. I agree that, for the many reasons we've discussed, in certain environments (art gallery/museum and similar viewing environments) the battle for incandescent/LED lighting is very likely worth the fight.